This application claims the priority of German application 199 48 249.7, filed Oct. 7, 1999, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a particular cooling system for an internal combustion engine in a motor vehicle. The cooling system includes a pipeline leading from the internal combustion engine to a radiator, a return pipeline leading from the radiator to the internal combustion engine, a bypass line connecting the pipeline and the return pipeline, and a thermostat valve, through which the coolant is passed. The invention also relates to an operating process for such a system.
This type of cooling system is known, for example, from German publication DE 37 05 232 A1. In such a system, the thermostat valve may contain, for example, an expansion element, which may or may not be heated. Reference is also made to German publication DE 43 24 178 A1 in connection with the feature of having different operating conditions lead to opening, partial opening and closing of the thermostat valve.
It is also known that, for checking whether the thermostat valve is in working order, a first temperature sensor for determining the inlet temperature of the thermostat and a second temperature sensor for determining the outlet temperature of the thermostat may be provided internally. In this construction, the inlet temperature of the thermostat corresponds to the temperature of the coolant at the outlet of the internal combustion engine, that is to the temperature of the coolant, which is to be cooled, and the outlet temperature of the thermostat corresponds to the coolant temperature at the outlet of the radiator, that is to the temperature of the cooled coolant, when the coolant has been passed at least partially through the radiator. During a checking routine, a defect in the thermostat valve is noted, firstly, if the inlet temperature of the thermostat is below the temperature at which the thermostat opens and the thermostat valve permits the coolant to flow back to the internal combustion engine only over the bypass, and, secondly, if there is a temperature difference between the outlet and inlet temperatures of the thermostat which is smaller than a specified error identification threshold. When the thermostat valve is in working order and the coolant temperature is below the thermostat opening temperature, the thermostat outlet temperature, as defined above, must be much lower than the thermostat inlet temperature. However, by this checking routine, only jamming of the thermostat valve can be recognized. Additional monitoring of the control temperature is not possible.
It is an object of the invention to provide a reliable diagnosis of the whole functioning capability of the thermostat valve in a cooling system of the type described above.
This objective is accomplished by providing at least one temperature sensor to determine the temperature of coolant at an outlet of the radiator, and supplying an output signal of the at least one temperature sensor to a control unit. When a first operating condition, for which the coolant must be passed by way of the thermostat valve initially only through the bypass line, changes to a second operating condition, for which the coolant is permitted to flow by way of the thermostat at least partially through the radiator, the control unit checks on whether an increase in the temperature of the coolant commences at the outlet of the radiator. Advantageous further developments of the invention are also reflected in the claims.
Thus, according to the invention, at least one temperature sensor is provided for determining the temperature of the coolant at the outlet of the radiator. The output signal of the temperature sensor is supplied to a preferably electronic control unit, which is already present anyhow in known cooling systems. Moreover, the output signal of the temperature sensor can be transferred either directly or, for example, over a bus connection from a different control device. The control unit, which usually also receives and processes other input signals, checks when there is a changeover from a first operating condition, during which the coolant would have to be passed through the thermostat valve initially only through the bypass line, to a second operating condition, for which the coolant would have to be released by the thermostat valve to flow at least partially through the radiator, and whether an increase in the temperature of the coolant is beginning at the outlet of the radiator.
Preferably, a second temperature sensor is provided in order to determine the temperature of the coolant at the outlet of the internal combustion engine. This second temperature sensor may be mounted, for example, in a cylinder head of the internal combustion engine. The output signal of this sensor is also supplied to a control unit. The most important operating conditions for opening, partially opening and closing the thermostat are related to the temperature of the coolant.
The second operating condition, which leads to the at least partial opening of the thermostat valve or to the partial release of coolant flow over the radiator, preferably is the attainment of a specified coolant temperature at the outlet of the internal combustion engine. This specified coolant temperature preferably is the so-called opening temperature. Further operating conditions may also relate, for example, to the ambient temperature or to the rotational speed of the internal combustion engine. The invention can be used for unheated thermostat valves as well as for thermostat valves, which can be heated.
The invention is based on the realization that, when the thermostat is functioning properly, the cooling water, before the opening temperature (the control temperature) is reached, flows exclusively in a so-called small cycle, that is, only through the bypass, avoiding the radiator. At the same time, the coolant temperature at the outlet of the radiator remains at an approximately constant level. When the operating condition, such as the opening temperature, is reached for opening the thermostat, the coolant flows for the first time, at least partially, through the radiator. As a result, the temperature of the coolant at the outlet of the radiator rises. If an increase in the temperature of the coolant at the outlet of the radiator is not recognized, although the thermostat would have had to be open in accordance with the specified operating conditions, then a fault indication may be put out in accordance with the known on-board diagnosis specifications. The fault indication may, for example, indicate a jamming of the thermostat valve in the closed state. In this case, the thermostat valve can be repaired.
The control unit preferably also checks whether the coolant temperature at the outlet of the internal combustion engine is above a second threshold, after the temperature of the coolant at the outlet of the radiator has reached or exceeded a first threshold. The first threshold is below the second threshold. An increase in the temperature of the coolant at the outlet of the radiator, for example by a specified amount, can be used as a reliable release condition for running the diagnosis required in the control operation. The second threshold advantageously is selected to correspond to specified environmental regulations, so that it corresponds to a coolant temperature or an internal combustion engine temperature, which is necessary at least for optimizing the emission values and/or for releasing further diagnosis functions relevant to the exhaust gas. If the coolant temperature at the outlet of the internal combustion engine in the control operation, that is, when the temperature of the coolant has already risen, is below this second threshold, then a fault indication is also put out. In this case, in a fault memory, a possibly wrong design of the thermostat valve or a leakage in the thermostat valve can be indicated. The thermostat valve accordingly must be replaced.
The invention makes it possible to perform an overall diagnosis with differentiated fault indications.
An embodiment of the invention is shown in the drawings.